Tense marking in English is relatively late appearing and is especially late for children with Specific Language Impairment (SLI). Little is known about the full course of acquisition for this set of morphemes. Because tense marking is a fundamental property of clause construction, it is central to current theories of morphosyntax and language acquisition. A longitudinal study is reported that encompasses the years of 2;6–8;9 years for typically developing children (N=43) and 4;6–8;8 years for children with SLI (N=21). The findings show that a diverse set of morphemes share the property of tense marking; that this set is not mastered until age 4 years in typically developing children and after 7 years for children with SLI; that acquisition shows linear and nonlinear components for both groups, in a typical S-shaped curve; and that nonsyntactic measures are not predictors of growth (including nonverbal intelligence, vocabulary size, and mother’s education), whereas initial MLU does predict rate of acquisition. The findings are consistent with a model of Optional Infinitives (OI) for typically developing children (cf. Wexler, 1994, 1996) and Extended Optional Infinitives (EOI) for children with SLI. This model hypothesizes incomplete specification of features of tense that are represented in the grammar.

Acknowledgments

Support for this investigation was provided by Grant NIDCD R01 DC01803. We wish to express our appreciation to the following doctoral level research assistants who contributed in multiple and important ways to the work reported here: Patricia Cleave, Karla Haney, Sean Redmond, Chien Wang, Su Dong Chen, and Laura Smith. In addition, we thank Hiromi Morikawa and Mary Howe, for their assistance with data management and analyses, and Esther Lerner, for data summaries and graphics. We also value greatly the assistance of Patsy Woods. We thank Carol Schekall, Candice Odle, Fiona Carswell, and Sara Tweed for assistance with data collection, transcription, and data entry. We are especially grateful for the support of the parents, who agreed to share their children for the purpose of investigation, and to the many teachers, school administrators, and preschool and day care providers who assisted us in the study. Although their contributions are worthy and each special in their own way, it is not possible to list names here because this list now numbers over 100 attendance centers. Preliminary reports of this investigation were presented at the Symposium on Research in Child Language Disorders, June 1997.

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